On this day in 1945, the United States, Great Britain, and China issue the Potsdam Declaration. The statement put the Japanese government on notice: The Allies were demanding unconditional surrender.
“The time has come,” the Allies declared, “for Japan to decide whether she will continue to be controlled by those self-willed militaristic advisers whose unintelligent calculations have brought the Empire of Japan to the threshold of annihilation, or whether she will follow the path of reason.”
Without unconditional surrender, the Allies warned, the Japanese would suffer “prompt and utter destruction.”
The Potsdam Declaration wasn’t the only thing happening that week. The American government was keeping track of many moving parts. We would be prepared to drop a nuclear bomb if the Japanese did not surrender.
One way or another, World War II would soon come to an end.
Truman had many reasons for such a decisive act. Obviously, he hoped to avoid an invasion of mainland Japan, if he could. Battles such as the one at Okinawa had demonstrated that a land invasion would result in massive bloodshed. But Truman may have had another interest, too: The Russian government had indicated that it could declare war on Japan by August 15.
Truman probably preferred to keep Russia out of any decision-making regarding post-war Japan. He’d already approached the Soviet leader, Joseph Stalin, and told him that the United States possessed a “new weapon of unusual destructive force.”
Stalin was unsurprised, although he apparently tried not to let on. His intelligence services already knew what was afoot in the United States! “The Russian Premier showed no special interest,” Truman later recalled.
Thus, even as Truman approved the Potsdam Declaration, many ships and planes were delivering bomb parts to the Pacific. One of these ships, USS Indianapolis, successfully carried parts for the Little Boy atomic bomb across the Pacific; it delivered its cargo on July 26. Mere days later, Indianapolis was torpedoed by a Japanese sub! Much of the crew was unfortunately stranded in the open ocean, but its vital mission had been accomplished.
Ultimately, as you know, Japan rejected the ultimatum that had been issued. Presumably, no one in Japan really knew what was coming at Hiroshima and Nagasaki. But you have to wonder whether anyone in America truly understood what was coming, either.
Bruce Cameron Reed, The History and Science of the Manhattan Project (2013)
Francis G. Gosling, The Manhattan Project: Making the Atomic Bomb (U.S. Dept of Energy; 1999) (reprint HERE)
Proclamation Defining Terms for Japanese Surrender (July 26, 1945)